Function max 

pub fn max<T: ArrowNumericType>(array: &PrimitiveArray<T>) -> Option<T::Native>
where
    T::Native: PartialOrd,

Returns the maximum value in the array, according to the natural order. For floating point arrays any NaN values are considered to be greater than any other non-null value

Example

let array = Int32Array::from(vec![4, 8, 2]);
let result = max(&array);
assert_eq!(result, Some(8));